Ultrasonic transducer for a proximity sensor

ABSTRACT

An ultrasonic transducer assembly for use in sensing the location of objects in proximity to the transducer. The ultrasonic transducer assembly includes a substrate member, a piezoceramic resonator plate supported on a planar surface of the substrate member adjacent to a peripheral edge of the substrate member, and a coupler connected to a surface of the resonator plate for acoustically coupling the resonator plate to a medium in contact with the coupler.

FIELD OF THE INVENTION

The present invention relates generally to ultrasonic transducers and, more particularly, to an ultrasonic transducer assembly that may be incorporated in a sensor to detect the presence and/or range of objects.

BACKGROUND OF THE INVENTION

Ultrasonic sensing systems provide an efficient and effective method of detecting objects, such as may be utilized in automated industrial manufacturing processes. These sensors require the use of a transducer to produce ultrasonic signals. For example, a transducer for such sensors typically generates an ultrasonic signal that is transmitted in the direction of an object, and a return or reflected signal is received by the transducer. A processor connected to the transducer processes the received signal and determines the presence and/or distance to an object based on the elapsed time between the transmitted and received signals.

Prior art piezoceramic ultrasonic transducers, such as those for use in air-based time-of-flight applications, have generally been designed to have very good long range detection capabilities. In designing these sensors, it has typically been considered desirable to maximize the Q value, i.e., the resonance, of the transducer and minimize the frequency of operation. A high Q value results in greater amplification of a returning signal, and low frequency serves to reduce the attenuation of ultrasound in air because attenuation is a function of frequency. Such prior art transducers have typically been configured as thin disks formed of ceramic material, which traditionally exhibit the benefit of a high Q value.

For various reasons, there are limitations on improving the efficiency and reducing the cost of manufacturing circular shaped ceramic disks, which in turn limits available cost reductions for components incorporating the ceramic disks, such as transducers incorporated into sensors. Accordingly, it is desirable to provide an alternative configuration for a sensor transducer that may incorporate a resonator component having a form factor or shape conducive to efficient production of both the resonator component and the assembled transducer.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, an ultrasonic transducer assembly is provided for use in sensing the location of objects in proximity to the transducer. The ultrasonic transducer assembly comprises a substrate member comprising a planar surface and a peripheral edge, a piezoceramic resonator plate supported adjacent to the planar surface, and a coupler connected to a surface of the resonator plate for acoustically coupling the resonator plate to a medium in contact with the coupler.

In accordance with another aspect of the invention, an ultrasonic transducer assembly is provided for use in sensing the location of objects in proximity to the transducer. The ultrasonic transducer assembly comprises a substrate member comprising a printed circuit board defining a planar surface and a peripheral edge, and a piezoceramic resonator plate including a planar inner surface supported on the planar surface adjacent to the peripheral edge. Electrical contacts are provided between the printed circuit board and the resonator plate for connecting the resonator plate to a power supply. The transducer further includes a coupler comprising a planar member including opposing first and second sides, the first side extending transverse to and connected to a surface of the resonator plate for acoustically coupling the resonator plate to a medium in contact with the second side of the coupler.

In accordance with a further aspect of the invention, a sensor is provided including an ultrasonic transducer assembly for use in sensing the location of objects in proximity to the transducer. The sensor comprises a substrate member comprising a printed circuit board defining a planar surface and a peripheral edge, and a rectangular piezoceramic resonator plate defining an elongated major dimension and a minor dimension. The resonator plate is supported in cantilever relation on the substrate member with its elongated major dimension extending from the peripheral edge of the substrate member. Electrical contacts are provided between the printed circuit board and the resonator plate for connecting the resonator plate to a power supply, one of said electrical contacts forming a cantilever support for said resonator plate on said substrate member. The sensor further includes a disk-shaped coupler comprising a planar member including opposing first and second sides. The first side extends transverse to and connects to a surface of the resonator plate. The coupler is acoustically excited by the resonator plate to transmit a signal to an object in proximity to the coupler, and the coupler receives and transmits reflected signals from the object to the resonator plate.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:

FIG. 1 is a side elevation view in partial cross-section of a sensor system incorporating a transducer assembly in accordance with the present invention;

FIG. 2 is an exploded perspective view of the transducer assembly in accordance with the present invention;

FIG. 3 is an enlarged cross-section view of the coupler end of the transducer assembly in accordance with the present invention;

FIG. 4 is an exploded perspective view showing assembly of a resonator plate to a printed circuit board substrate for the transducer assembly in accordance with the present invention

FIG. 5 is an enlarged cross-section view of the coupler end of a transducer assembly in accordance with an alternative embodiment of the present invention;

FIG. 6 is an exploded perspective view the alternative embodiment of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.

Referring to FIG. 1, there is shown an ultrasonic sensor 10 for determining the presence and distance of an object 12 in proximity to the sensor 10. The sensor comprises a housing 14 and a transducer assembly 16, and including a damping material 18 surrounding the transducer assembly 16 within the housing 14, as will be described further below.

Referring to FIG. 2, the transducer assembly 16 includes a substrate member 20 defined by a printed circuit board, a transducer or resonator plate 22, and a plate-like coupler or coupling assembly 24 connected to and extending transversely to the resonator plate 22. The coupling assembly 24 provides an ultrasonic interface between the relatively small resonator plate 22 and a medium, such as air, filling the space between the sensor 10 and the object 12, as depicted by the region 15 in FIG. 1.

The resonator plate 22 may be constructed from any suitable piezoelectric material. In a preferred embodiment, the resonator plate 22 comprises a piezoceramic plate. In particular, the resonator plate 22 may be constructed from a lead zirconate titanate, such as PZT5A which may be obtained from, for example, Morgan Electro Ceramics, Bedford, Ohio. Desirable characteristics associated with a piezoceramic material for the present application include high mechanical-to-electrical conversion efficiency, a substantially flat temperature response, and a relatively high mechanical quality factor (Qm) which in the present example is approximately 75.

Referring further to FIG. 3, the coupling assembly 24 comprises a substantial surface area for transferring ultrasonic energy from the resonator plate 22 to the medium. In the illustrated embodiment, the coupling assembly 24 comprises a diaphragm 26 defining a first side 28 of the coupling assembly 24. The diaphragm 26 is capable of vibrating in response to vibratory energy from the resonator plate 22. The diaphragm 26 comprises a stiff or rigid material and may be formed of a variety of materials including, without limitation, metal, plastic, or a polymer, e.g., a molded thermoset polymer such as an epoxy. In one preferred embodiment, the diaphragm 26 may be formed of a thin plate of stainless steel. As illustrated herein, the diaphragm 26 of the present embodiment is a thin or plate-like, disk-shaped member where the vibratory energy from the resonator plate 22 is substantially distributed in a direction that is orthogonal to said substrate member 20. That is, the acoustic vibratory signals travel along a path directed circumferentially and radially from a central location on the diaphragm 26, defined at an aperture 30 in the diaphragm 26, to an outer edge of the diaphragm 26. It should be understood that the diaphragm 26 is not limited to a disk-shaped member and may comprise a plate-like member embodying other shapes.

The coupling assembly 24 may further include an impedance matching member 32, illustrated herein as a disk-shaped member located over the diaphragm 26. The impedance matching member 32 defines a second, outwardly facing side 34 of the coupling assembly 24. The impedance matching member 32 comprises a material selected to maximize coupling of the ultrasonic energy from the resonator plate 22 to the medium 15, and is typically a different material than the material of the diaphragm 26. For example, the impedance matching member 32 may comprise a relatively resilient material such as rubber, an epoxy material, a polymer, glasses, or combinations and/or mixtures of these materials. In a preferred embodiment for interfacing with an air medium, the impedance matching member 32 comprises a glass-filled epoxy member. It should be understood that although air is referenced as a medium for the purposes of describing the present embodiment, the material and construction of the impedance matching member 32 may be selected such that the impedance matching member 32 is configured to couple to other media including liquids or other gases. In addition, the impedance matching member 32 is not limited to the illustrated disk-shaped configuration and may comprise other shapes such as, for example, a shape matching the shape of the diaphragm 26.

As seen in FIGS. 2 and 3, the impedance matching member 32 includes a recess area 31 for receiving the diaphragm 26. The surface of the diaphragm 26 opposite the first side 28 is positioned in engagement with a surface 33 of the impedance matching member 32 with the recess 31 for transmittal of ultrasonic signals between the diaphragm 26 and the impedance matching member 32.

It should further be understood that in some applications of the sensor 10 described herein, it may be possible to construct the coupling assembly 24 without an impedance matching member 32. For example, the coupling assembly 24 may be constructed with the material of the diaphragm 26 selected to provide a satisfactory coupling to effectively deliver and receive ultrasonic energy to and from the medium.

An isolation member 35 is located adjacent to the first side 28 of the coupling assembly 24, i.e., behind the impedance matching member 32 and the diaphragm 26. The isolation member 35 is preferably formed of a resilient material and provides an isolation layer or barrier for isolating at least the diaphragm 26, and preferably both the diaphragm 26 and impedance matching member 32, from the damping material 18 within the housing 14. In a preferred embodiment, the damping material 18 comprises a urethane material and the isolation member 35 comprises a silicon rubber material, i.e., a silicon foam rubber, and has a circular configuration with a central aperture 37. The isolation member 35 preferably has an outer diameter that substantially matches the diameter of the coupling assembly 24.

As seen in FIG. 2, the substrate member 20 is configured as an elongated rectangular element comprising an upper planar surface 36, a lower planar surface 38, and a peripheral edge 40 defined by opposing generally parallel side edges 42, 44 and by opposing generally parallel front and rear edges 46, 48, respectively. A tongue or peninsula portion 50 extends in cantilever relation from the front edge 46 centrally between the side edges 42, 44.

Referring further to FIG. 4, the resonator plate 22 is shown as comprising an elongated plate-like element having a substantially planar inner surface 52, a substantially planar outer surface 54, a front edge 56, a rear edge 58, and opposing side edges 60, 62. A major dimension D₁ is defined between the front and rear edges 56, 58, and a minor dimension D₂ is defined between the opposing side edges 60, 62. The resonator plate 22 is positioned with its inner surface 52 located on or adjacent to the upper surface 36 of the substrate member 20, and with its major dimension D₁ extending from the front edge 46 of the substrate member 20 over the peninsula portion 50. The front edge 56 of the resonator plate 22 is located adjacent a front edge 59 of the peninsula portion 50. The minor dimension D₂ of the resonator plate 22 is substantially equal to a width of the peninsula portion 50, as measured between opposing sides 64 and 66 of the peninsula portion 50.

The resonator plate 22 is oriented parallel to the substrate member 20 and is preferably positioned on a first contact pad 68 located on the substrate member 20 to form an electrical contact between the inner surface 52 and the first contact pad 68. The contact pad 68 preferably comprises a raised portion that extends above the substrate member 20 for supporting the resonator plate 22 in cantilever relation, spaced from the substrate member 20. Hence, there is preferably an air gap between the inner surface 52 of the resonator plate 22 and the upper surface 36 of the substrate member 20. In addition, a top wire 70 is provided extending between the outer surface 54 and a second contact pad 72 on the substrate member 20. The first and second contact pads 68, 72 comprise conductors electrically connected to a power supply 74 and processor 76 (see FIG. 2) on the substrate member 20. The electrical connections from the contact pads 68, 72 may be formed by respective electrical strip lines 69, 73 etched on the printed circuit board defining the substrate member 20, see FIGS. 2 and 4. It should be understood that either or both the power supply 74 and processor 76 may be defined by a printed circuit board structure on the substrate member 20 in a conventional manner or, alternatively, may be located remotely from the substrate member 20.

Although the preferred embodiment comprises a single support, i.e., the first contact pad 68, for supporting the resonator plate 22, the resonator plate 22 may be supported by one or more additional supports. For example, the resonator plate 22 may be supported on a pair of supports located adjacent longitudinal ends of the resonator plate 22, where at least one of the supports preferably forms an electrical contact to the electrical strip line 69.

In a process for assembling the transducer assembly 16, the resonator plate 22 may be assembled to the substrate member 20 by an apparatus performing a pick-and-place operation to locate the resonator plate 22 on the peninsula portion 50 and extending over the first contact pad 68. The top wire 70 may be assembled to the substrate member 20 in an automated operation, such as an operation performed by feeding a plurality of prepared top wires 70 in a conventional tape and reel supply configuration. Each successive top wire 70 may be placed with a vertical portion thereof in engagement with the second contact pad 72, and with a horizontal portion of the top wire 70 engaged over the upper surface of the resonator plate 22 to form an electrical contact between the outer surface 54 and the electrical conductor 73 of the printed circuit board via the second contact pad 72, see FIG. 4. In the illustrated embodiment, a hole is shown in the second contact pad 72 for receiving the vertical portion of the top wire 70, however, such a hole is not required for implementation of the present invention.

The assembly of the resonator plate 22 to the substrate member 20 may be performed in an assembly method that includes placement of other components on the substrate member 20. Specifically, the resonator plate 22 and top wire 70 may be placed on the printed circuit board defining the substrate member 20, along with other components including those forming the processor 76 and power supply 74, and subjected to a conventional surface mount technology (SMT) reflow process to connect the components to the printed circuit board. Hence, one side of the resonator plate 22 is directly attached to the printed circuit board of the substrate member 20 through the SMT reflow process. Further, the SMT reflow attachment of the resonator plate 22 provides a high integrity attachment that generally requires fewer parts and reduced labor, as compared to known assemblies and processes typically implemented for attachment of prior art piezoceramic ultrasound components to circuit boards or similar mounting structures.

Subsequent to mounting the resonator plate 22 to the substrate member 20, the coupling assembly 24 is attached to at least the outer surface 54 of the resonator plate 22 adjacent to the front edge 56, and extending in orthogonal relation to the plane of the resonator plate 22. Specifically, the central aperture 30 in the diaphragm 26 is positioned over the end of the resonator plate 22, and the front edge 56 of the resonator plate 22 is positioned in engagement with or closely adjacent to an inner face 33 of the impedance matching member 32. In addition, the isolation member 35 is positioned at the first side 28 of the coupling assembly 24, with the resonator plate 22 extending through its central aperture 37. In a preferred embodiment, the diaphragm 26 and impedance matching member 32 are bonded to the resonator plate 22 such that the inner surface 33 of the impedance matching member 32 is bonded to the front edge 56 of the resonator plate 22. In addition, bonding will also typically occur between the other surfaces of the resonator plate 22, i.e., inner and outer surfaces 52 and 54 and side edges 60, 62, the surfaces 36, 38, 59, 64 and 66 on the peninsula portion 50, and the surface of the diaphragm 26 adjacent the aperture 30. In other words, all adjacent surfaces of the diaphragm 26, the resonator plate 22 and the peninsula portion 50 may be joined by the bonding. Typically, the bonding may be accomplished via an epoxy bond 80 applied at the end of the resonator plate 22 forming a mechanical connection between the resonator plate 22 and the diaphragm 26 and impedance matching member 32 components of the coupling assembly 24, as well as to adhere the isolation member 35 to the first side 28 of the coupling assembly 24. The epoxy bond 80 additionally affixes the coupling assembly 24 to the peninsula portion 50 of the substrate member 20, such that the coupling assembly 24 is supported from the substrate member 20 with the first side 28 of the coupling assembly 24 adjacent to and spaced from the front edge 46 of the substrate member 20.

Accordingly, transmission of ultrasonic energy between the resonator plate 22 and the coupling assembly 24 is facilitated by the mechanical connection formed by the epoxy bond 80. Through the coupling to the resonator plate 22, the coupling assembly 24 exhibits good transmittance and impedance matching to the medium at the operating frequencies of the resonator plate 22, which in the presently described embodiment may be in the range of approximately 100 kHz to approximately 1 MHz.

An advantage of the construction of the transducer assembly 16 described herein relates to the construction of the resonator plate 22 and its assembly to the substrate member 20. Specifically, the geometric configuration of the resonator plate 22 is such that a plurality of the resonator plates 22 may be obtained from a single sheet of ceramic material. In particular, a sheet of ceramic material such as, for example, PZT5A may be manufactured and scored or cut to form a plurality of individual rectangular pieces substantially corresponding to the desired dimensions of the resonator plate 22. Hence, multiple resonator plates 22 may be manufactured with minimal waste or residual material, as compared to formation of prior art disk-shaped transducer resonators which necessitate more steps to form to the desired shape, as well as less efficient use of materials.

Further, as noted above, the placement of the resonator plate 22 parallel to the substrate member 20 facilitates automated assembly of the transducer assembly 16, such as by means of a conventional pick-and-place assembly operation. In contrast, known assembly operations for assembly of transducer resonators that are not mounted in parallel relation to the mounting structure, i.e., printed circuit board, often require operator handling of the ceramic resonator to effectively place the resonator relative to the mounting structure. Accordingly, a combination of efficiencies in the present transducer design contribute to an easily manufactured and economical assembly.

It should be noted that the present invention is not necessarily limited to the particular rectangular shape described herein for the resonator plate 22. Hence, other shapes may be selected for the resonator plate 22, although a resonator plate 22 having a form factor that facilitates economical manufacture of the resonator plate 22 is preferred.

An example of an alternative embodiment of the present invention is illustrated in FIGS. 5 and 6 in which a disk-shaped resonator plate 122 is supported on a substrate member 120 in a manner similar to that described for the embodiment illustrated in FIGS. 1-4, and in which elements of the embodiment of FIGS. 5 and 6 corresponding to the embodiment of FIGS. 1-4 are labeled with the same reference numeral increased by 100.

The resonator plate 122 preferably comprises a piezoceramic plate, similar to the material described above for the resonator plate 22. The resonator plate 122 may be supported on a first contract pad 168 such that the resonator plate 122 is supported in spaced relation to an upper planar surface 136 of the substrate member 120, with an air gap between the resonator plate 122 and the substrate member 120. Preferably, the first contact pad 168 engages the resonator plate 122 at the geometric center of the resonator plate 122 and may be attached by a solder connection 167, such as may be implemented by an SMT reflow process, to form an electrical connection between an electrode on the inner surface 152 of the resonator plate 122 and the first contact pad 168. Hence, the resonator plate 122 is supported in cantilever relation on the first contact pad 168. A second electrical connection to an electrode on the outer surface 154 of the resonator plate 122 may be provided by a top wire 170 extending to a contact pad 172 on the substrate member 120, and may be connected via an SMT reflow process.

A coupler 124 comprising, for example, a glass-filled epoxy member is located on the outer surface 154 of the resonator plate 122 to provide impedance matching between the resonator plate 122 and a medium. The coupler 124 may be provided with a recess for accommodating the top wire 170 where it is attached to the top surface 154 of the resonator plate 122. The path for acoustic signals transmitted from and received by the resonator plate 122 and coupler 124 extends in a direction that is generally orthogonal to the planar surface 136 of the substrate member 120. It may be noted that in the present embodiment, the coupler 124 is constructed without a diaphragm in that the resonator plate 122 substantially distributes the vibrational energy across the entire area of the coupler 124, without requiring a diaphragm to distribute the energy in the radial direction.

In addition, a support or support ring 180 may be located on the substrate member 120 substantially aligned with at least a portion of an outer peripheral portion of the inner surface 152 of the resonator plate 122. The support ring 180 extends above the plane of the planar surface 136, and includes an upper surface 182 that is preferably spaced a relatively small distance from the inner surface 152 of the resonator plate 122. The support ring 180 may be engaged by the inner surface 152 to limit the cantilever forces that may be exerted at the mounting point with the first contact pad 168.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. 

1. An ultrasonic transducer assembly for use in sensing the location of objects in proximity to the transducer, said ultrasonic transducer assembly comprising: a substrate member comprising a planar surface and a peripheral edge; a piezoceramic resonator plate supported adjacent to said planar surface; and a coupler connected to a surface of said resonator plate for acoustically coupling said resonator plate to a medium in contact with said coupler; wherein said resonator plate is supported in cantilever relation on a contact pad extending in spaced relation generally parallel to said substrate member.
 2. An ultrasonic transducer assembly for use in sensing the location of objects in proximity to the transducer, said ultrasonic transducer assembly comprising: a substrate member comprising a planar surface and a peripheral edge; a piezoceramic resonator plate supported adjacent to said planar surface; and a coupler connected to a surface of said resonator plate for acoustically coupling said resonator plate to a medium in contact with said coupler; wherein said resonator plate comprises a rectangular plate defining an elongated major dimension and a minor dimension and said coupler is attached adjacent an end of said major dimension.
 3. An ultrasonic transducer assembly for use in sensing the location of objects in proximity to the transducer, said ultrasonic transducer assembly comprising: a substrate member comprising a planar surface and a peripheral edge; a piezoceramic resonator plate supported adjacent to said planar surface; and a coupler connected to a surface of said resonator plate for acoustically coupling said resonator plate to a medium in contact with said coupler; wherein said coupler comprises a substantially rigid plate-like diaphragm member extending transverse to said resonator plate.
 4. The ultrasonic transducer assembly of claim 3, wherein said coupler further comprises an impedance matching member extending over said plate-like member.
 5. The ultrasonic transducer assembly of claim 4, wherein said diaphragm member includes an aperture and said resonator plate extends to said aperture, and including a bonding structure mechanically connecting said surface of said resonator plate to said diaphragm member and to said impedance matching member.
 6. The ultrasonic transducer assembly of claim 5, wherein said diaphragm member comprises a disk-shaped member.
 7. The ultrasonic transducer assembly of claim 5, including a damping material located on a side of said coupler opposite said medium, and including a resilient isolation layer separating said diaphragm member from said damping material.
 8. The ultrasonic transducer assembly of claim 1, wherein said substrate member comprises a printed circuit board, and said resonator plate is electrically connected to said printed circuit board through a surface mount technology contact formed between said planar surface of said substrate member and a planar inner side surface of said resonator plate.
 9. The ultrasonic transducer assembly of claim 8, including an electrical conductor extending between an outer side of said resonator plate, opposite said inner side, and said printed circuit board.
 10. The ultrasonic transducer assembly of claim 9, wherein said coupler comprises a generally planar member extending transverse to said resonator plate.
 11. The ultrasonic transducer assembly of claim 1, wherein said substrate member includes a peninsula portion extending in cantilever relation from said peripheral edge of said substrate member and defines a portion of said planar surface.
 12. The ultrasonic transducer assembly of claim 1, wherein said resonator plate comprises a disk-shaped member and is soldered to said contact pad at a geometric center portion of said resonator plate.
 13. The ultrasonic transducer assembly of claim 1, wherein said coupler is bonded to a planar surface of said resonator plate such that a path for acoustic signals transmitted from and received by said resonator plate extends in a direction that is orthogonal to said planar surface of said substrate member.
 14. An ultrasonic transducer assembly for use in sensing the location of objects in proximity to the transducer, said ultrasonic transducer assembly comprising: a substrate member comprising a printed circuit board defining a planar surface and a peripheral edge; a piezoceramic resonator plate including a planar inner surface supported at said planar surface adjacent to said peripheral edge; electrical contacts between said printed circuit board and said resonator plate for connecting said resonator plate to a power supply; and a coupler comprising a planar member including opposing first and second sides, said first side extending transverse to and connected to a surface of said resonator plate for acoustically coupling said resonator plate to a medium in contact with said second side of said coupler.
 15. The ultrasonic transducer assembly of claim 14, wherein said resonator plate comprises a rectangular plate defining an elongated major dimension and a minor dimension, and said resonator plate is supported in cantilever relation on a contact pad with its elongated major dimension extending from said peripheral edge of said substrate member.
 16. The ultrasonic transducer assembly of claim 14, wherein said coupler comprises a substantially rigid disk-shaped diaphragm and an impedance matching member of a different material than said diaphragm extending over said diaphragm and defining said second side, and said coupler further includes a bonding structure mechanically connecting said surface of said resonator plate to said diaphragm and said impedance matching member at said first side.
 17. The ultrasonic transducer assembly of claim 16, including a damping material surrounding said substrate member, said resonator plate and said coupler, and said coupler further comprises a resilient isolation layer separating said diaphragm from said damping material.
 18. A sensor including an ultrasonic transducer assembly for use in sensing the location of objects in proximity to the transducer, said sensor comprising: a substrate member comprising a printed circuit board defining a planar surface and a peripheral edge; a rectangular piezoceramic resonator plate defining an elongated major dimension and a minor dimension, said resonator plate being supported in cantilever relation on said substrate member with its elongated major dimension extending from said peripheral edge of said substrate member; electrical contacts between said printed circuit board and said resonator plate for connecting said resonator plate to a power supply, one of said electrical contacts forming a cantilever support for said resonator plate on said substrate member; and a disk-shaped coupler comprising a planar member including opposing first and second sides, said first side extending transverse to and connected to a surface of said resonator plate, said coupler being acoustically excited by said resonator plate to transmit a signal to an object in proximity to said coupler, and said coupler receiving and transmitting reflected signals from said object to said resonator plate.
 19. The sensor of claim 18, wherein said coupler comprises a substantially rigid diaphragm and an impedance matching member of a different material than said diaphragm extending over said diaphragm and defining said second side, and said coupler further includes a bonding structure mechanically connecting said surface of said resonator plate to said diaphragm and said impedance matching member at said first side.
 20. The sensor of claim 19, including a housing containing a damping material surrounding said substrate member, said resonator plate and said coupler, and said coupler further comprises a resilient isolation layer separating said diaphragm from said damping material. 